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Discussion Starter #1
Has anybody else had to replace their front oxygen sensor recently?

A couple of months back my car dropped into limp home mode while I was driving on the interstate. A little disconcerting but my XV kept chugging along albeit with much reduced gas mileage.

I took it straight to my local Subaru specialist and they couldn't figure out what was wrong with it. They finally called the local Subaru dealer to see if they could get any clues and decided it had to be the front oxygen sensor.

I didn't have the resources at the time to get that replaced and just followed their recommendations to use top tier, mid grade (89 octane) gasoline until I could bring it back in for a replacement with the strong warning that I was shortening the life of my catalytic converter the longer I waited.

In the three months I drove on the "failed" front sensor the car never dropped back into limp home mode again but the fuel economy never fully recovered. (The 28.8 mpg highway driving including the expected drop associated with winter driving.) I also purchased an ODB II bluetooth reader and app to monitor performance on my phone. Sure enough, O2 sensor #1 was ready nothing....

So, I finally took it back in to get the oxygen sensor replaced and viola! Fuel economy recovered dramatically....for about 8 days... then it tanked again. Still no limp home mode but another look at the ODB II and sure enough the O2 sensor is reading nothing.

I am going to double check my tire pressure and my intake air filter in the mean time....

What is the typical impact of temperature on mileage for you all?

Have any of you had similar issues?
 

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Recently, my local Subaru mechanic informed me that the caked-on mud around the catalytic converter and oxygen sensor are not to be left like that, as it may have an adverse effect on the readings.

I'm assuming corrosion and other materials around the O2 sensor may have played into your current predicament.
 

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Discussion Starter #3
Yeah, I've had to frequently drive across a salty winter pass. I've made a habit of thoroughly washing the car after each trip but that's just a mitigating tactic really.

Interestingly enough, I took by the shop and they showed me that the new front O2 sensor appeared to be running just fine. My bluetooth ODB II sensor wasn't reading the constant voltage signal I guess as well as confirming that I am a bit of a car hypochondriac.

They kept trying to get me to run midgrade but I've found that using it induces both a metallic pingy rattle upon acceleration and leadens my right foot.

Also, signing into to Fuelly helped reset my mileage expectations. What an awesome amount of data....
 

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You should be able to run regular fuel and not hear any "pingy rattle" while accelerating.If you must run mid grade or premium fuel to eliminate that ping/rattle then you have a problem with pre ignition.The knock sensor isn't detecting that ping/rattle.If it did then the ECU would have retarded the ignition timing making the plugs fire later to stop that ping.I would say the issue lies in the knock sensor,the ECU or the connection between the two.
 

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I think i am having this issue. I got a OBDLink car scan tool as a gift and it says i am getting no power to the front O2 sensor. I get no check engine lights or Faults on the scanner. My mileage has taken a real nose dive as well. Has anyone else had this issue?
 

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The recent loss of mileage thing could be the switch over to "winter" gas. But it should be a fairly minimal amount overall- maybe 2-3 mpg possibly more depending on your driving habits.
They usually start distributing the winter stuff around 1st of October or thereabouts. Might be earlier in colder climates.
 

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The recent loss of mileage thing could be the switch over to "winter" gas. But it should be a fairly minimal amount overall- maybe 2-3 mpg possibly more depending on your driving habits.
They usually start distributing the winter stuff around 1st of October or thereabouts. Might be earlier in colder climates.

This has been going on for a while so it is not the fuel change.
 
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